The present invention relates to a variable distribution type automotive headlamp in which the light distribution pattern can be controlled so as to be most suitable for current $ operating conditions. More particularly, the invention relates to such headlamps provided with a light source such as a single-filament type bulb.
Conventionally, variable distribution type headlamps use a double-filament type bulb mounted so that the two filaments Io are aligned with the forward optical axis of a reflector. The two filaments are selectively illuminated so as to change the diffusion angle of the luminous flux to thereby change the light distribution pattern, so that a main beam and a sub-beam are obtained.
However, a headlamp having a structure has a problem that a reflector having reflecting surfaces corresponding to two filament positions must be provided, as a result of which the structure of the reflecting surfaces becomes complicated. Moreover, the reflection direction of the luminous flux differs o depending on the bulb mounting position, so that sometimes a suitable light distribution pattern cannot be obtained.
FIG. 16 shows a lamp of the above type in which the direction of the luminous flux can be changed in the horizontal direction, as disclosed in U.S. Pat. No. 3,333,094. The lamp includes a bulb 51 provided at the focal point F of a reflector 50 having a parabolic reflecting surface. The front surface of the lamp is covered with a front lens 52. A plurality of pivotally mounted reflecting plates 53 provided between the front lens 52 and the reflector 50 can be rotated to the left or right (through an angle .phi.), so that the output light flux is swung left/right (through an angle of 2.phi.) so as to be suitably directed for operating conditions such as driving on a curved road or the like. lD In such a distribution type headlamp as described above, however, the luminous flux which can be controlled by the reflecting plates 53 increases as the rotation angle .phi. increases, so that the effect for improving visibility is small in the case where the rotation angle .phi. of the reflecting plates 53 is small. Further, not only does the loss of light due to the plate thickness of many reflecting plates 53 become large, but the focal length of the reflector 50 is relatively short, so that the image of the filament of the bulb 51 becomes large. As a result, there is a problem that the vertical width of the zo luminous flux deflected by the respective reflecting plates 53 is so large that an improvement in distant visibility cannot be obtained.